Our long-term objectives remain to elucidate in molecular detail the structure, stability and dynamic[unreadable] properties of the plasma lipoproteins and apolipoproteins that are vital to an understanding of lipid[unreadable] interactions, apoprotein exchange, lipoprotein-cell-surface interactions, receptor-mediated lipoprotein uptake,[unreadable] and lipoprotein inter-conversions. The conformational adaptability of the exchangeable apoproteins is[unreadable] essential to both their structural role in lipoprotein stabilization and their functional roles as cofactors for[unreadable] enzymes, ligands for receptors, or mediators of reverse cholesterol transport. A detailed understanding of[unreadable] apoprotein structural stability and adaptability is vital to further progress in understanding lipoprotein[unreadable] structure and function. The precise molecular mechanisms of this unique structural adaptability remain[unreadable] unclear, and remain the focus of the proposed research. Continuing our previous work, we will focus on[unreadable] structural investigations of lipoproteins (HDL and LDL) and apolipoproteins to highest possible resolution,[unreadable] using state-of-the-art methods of molecular biophysics and structural biology. The structure and stabilizing[unreadable] interactions of synthetic or expressed peptides that model important structural and functional units in the[unreadable] sequences of the exchangeable apoproteins (primarily apoA-l) will be determined. These peptides are[unreadable] designed based on the 11/22 residue helical segments comprising native apoA-l, and on an "idealized"[unreadable] consensus sequence for the fundamental 11/22-mer tandem repeat in the sequence of the exchangeable[unreadable] apoproteins. Structural and thermodynamic studies of mutant forms of apoA-l encompassing point and[unreadable] deletion mutants will concentrate on the role of specific regions of the apoA-l molecule in its conformation[unreadable] and stability. The three-dimensional structure of intact LDL, with emphasis on the topology and the molecular[unreadable] conformation of the apo-B100 at the lipoprotein surface will be determined by cryo-electron microscopy and[unreadable] 3D-image reconstruction. The focus will be on the organization of apo-B and the localization of structural and[unreadable] functional domains on the LDL particle, using a combination of site-specific immuno-labeling and direct[unreadable] visualization of the bound LDL receptor. The structure of the LDL receptor domains with and without bound[unreadable] apoE and/or apoB peptides will be determined using crystallographic methods. This should ultimately lead to[unreadable] understanding the molecular mechanisms underlying the physiological functions of plasma lipoproteins and[unreadable] lead to the development for molecular approaches to the prevention of heat disease and atherosclerosis.